An anodic oxidation method is known in which an oxide film having a predetermined thickness is artificially generated on a base surface of aluminum, for example. According to this method, an electrolytic solution having a strongly acid property such as sulfuric acid and oxalic acid is received in a treatment vessel, an aluminum-made object to be treated is received in this electrolytic solution, and an oxide film is formed on the base surface of the aluminum by oxidation reaction with the electrolytic solution serving the object as an anode (see, for example, Patent Document 1).
However, this conventional oxide film generating method has such problems that an electrolytic solution having a strongly acid property such as sulfuric acid and oxalic acid is required, a special water discharging equipment is required for discharging the electrolytic solution, thus increasing the production cost and equipment cost, and operation is obliged to be conducted under such a circumstance that a toxic gas is generated.
Moreover, in case an oxide film having a high degree of hardness is to be generated, the temperature of the treatment vessel must be set to low, and in order to prevent increase in temperature due to heat radiation at the time of growth of the oxide film, a cooling equipment and its cooling operation are required. Thus, the production cost and the equipment cost are increased, and productivity is decreased.
Incidentally, the oxide film comprises a porous bulk layer and a barrier layer composed of an amorphous alumina (Al2O3), and the bulk layer on the outer surface side has a plurality of pores formed therein. However, since the oxide film itself is poor in corrosion resistance and it has a white or colorless transparent color, it is a normal practice to conduct the sealing treatment in order to enhance the corrosion resistance and the dyeing treatment in order to enhance the decorative property.
Of all, the sealing treatment employs a method in which the oxide film is treated with a high temperature pressurized water vapor or boiled in a boiled water so that the pores are sealed or reduced in size (for example, Patent Document 2). In the dyeing treatment, after the oxide film is generated, it is electrolyzed in a solution with metal salt dissolved therein so that metal or metal compound is deposited in the pore and then dyed (see, for example, Patent Document 3).
However, the above-mentioned sealing treatment has such problems that a treatment vessel is required separately from the anodic oxidation treatment vessel and an object to be treated must be shifted to another vessel after the anodic oxidation is carried out, thereby the equipment cost is increased and the process becomes complicated.
Moreover, since the conventional sealing treatment generally aims at improvement of corrosion resistance, it is difficult to realize an ornamental processing of high quality and a processing which satisfies both the corrosion resistance and ornamental property.
The adjustment or management of such corrosion resistance and ornamental property is performed by means of generation of the oxide film, the number of pores, and the sealing treatment. However, it is difficult to obtain a predetermined oxide film by adjusting the density of electric current. It is also difficult to adjust the diameter of the pores by hydration treatment through temperature management.
On the other hand, the above-mentioned oxide film draws attention in various fields as a catalyst body capable of carrying various kinds of catalysts. Many proposals have been made as to a method for manufacturing a catalyst body.
In the method for manufacturing a catalyst body, for example, an alumina layer is formed on the surface of an aluminum as a base by anodic oxidation, thus obtained alumina layer is subjected to hydration treatment at 10 degrees C. through 80 degrees C., after the diameter of pores is enlargingly adjusted to 200 A through 400 A, the resultant is immersed into a solution containing a silica source, then baked at 300 degrees C. through 550 degrees C., and after baking, a catalyst is carried on the silica coating surface (see, for example, Patent Documents 4 and 5).
However, the conventional method for manufacturing a catalyst body requires various processes and temperature management, and is thus complicated and time and labor consuming. Moreover, the equipment cost is increased and the manufacturing cost is also increased. In addition, it is difficult to obtain a sufficient precision in adjustment of enlargement of the diameter of the pores by hydration treatment and the yield of production is inferior.
On the other hand, recently, utilization of an optical catalyst have drawn attention in various fields. Of all, utilization and development of titanium oxide draw attention.
Regarding titanium oxide, various manufacturing method have heretofore been proposed. Of all, as a manufacturing method utilizing an anodic oxidation method, there is known a method in which, for example, a pure titanium-base material or titanium-based alloy material is anodically oxidized in a diluted acidic solution such as phosphoric acid and after this anodic oxidation, the resultant is heated at 300 degrees C. through 800 degrees C. in an acidic atmosphere (see, for example, Patent Document 6).
However, in the method for manufacturing titanium oxide, the discharge of exhaust solution is restricted in the process of anodic oxidation as it contains an environmental pollutant.
Since phosphoric acid is used, a special water discharge processing equipment is required and thus, the equipment cost is increased and the manufacturing cost is also increased.
Incidentally, as means for cleaning the exhaust gas discharged from automobiles and for capturing an odor substance, there is known an alumite catalyst reacting device in which the device wall of a reaction chamber for allowing the gas, which is to be cleaned, to be flowed therein is subjected to alumite treatment and a catalyst is carried on the alumite treated surface. And as its catalyst, a metal catalyst such as a metal of platinum group and its alloy, gold and palladium is used (see, for example, Patent Documents 4, 5 and 7).
Of all, palladium is generated from palladium chloride and widely used as its catalytic effect is high. However, since palladium has low solubility with water and it forms a hydrate in an aqueous solution, its catalyst carrying capability is lowered.
So, it is a normal practice that palladium is dissolved in an organic solvent such as acetone and ethanol so that its catalyst carrying capability is increased. Therefore, the catalyst carrying solution becomes expensive and alumite is eroded at the time palladium chloride is dissolved in an acidic solution such as hydrochloric acid and carried on the alumite. For this reason, it is difficult to employ palladium.